1. Field of the Invention
The present invention relates to a magnetic toner for MICR printers, a developer for MICR printers and a manufacturing method thereof, and, more specifically, concerns a magnetic toner for MICR printers and a developer for MICR printers which, even after, for example, 150,000 to 300,000 sheets of A4-paper have been continuously printed, still provide superior image density and reading precision, and a manufacturing method thereof.
2. Description of the Background Art
In recent years, with respect to checks, securities, bills, tickets, etc., in order to prevent counterfeit and illegal copies thereof, identification marks referred to as xe2x80x9cfontsxe2x80x9d have come to be printed. This counterfeit prevention system using such identification marks is generally referred to as MICR system (Magnetic Ink Character Recognition System), and toner used for printing these fonts by the electrophotographing system is referred to as magnetic toner for MICR printers (in some cases, referred to simply as MICR toner or magnetic toner). These are, for example, disclosed in Japanese Laid-Open Patent Application No. 134648/1990, Japanese Laid-Open Patent Application No. 80582/1993 and U.S. Pat. No. 5,034,298.
However, the conventional MICR toner tends to have problems of low image density and susceptibility to reading errors. Moreover, since the MICR toner contains special magnetic powder, it tends to have high values in the specific gravity and residual magnetization and to form aggregation, resulting in degradation in the fluidity and transporting property.
In order to solve these problems, Japanese Laid-Open Patent Applications No. 358164/1992, No. 358165/1992 and No. 77829/1995 have disclosed MICR toners which use two types of magnetic powders so that the residual magnetization is set in the range of 4.0 to 7.0 emu/g.
However, these MICR toners are still susceptible to reading errors, need to increase the image density, and are inferior in durability, and another problem is that magnetic power contained therein is inferior in the dispersing property.
Therefore, the inventors of the present invention have filed Japanese Patent Application No. 137153/1998 which has proposed an MICR toner that contains first magnetic powder having a residual magnetization of 24 to 40 emu/g and second magnetic powder having a residual magnetization of 1 to 24 emu/g (where 24 emu/g is not included) so that the residual magnetization of the entire toner is set to 7 to 20 emu/g (where 7 emu/g is not included), and that consequently achieves superior image density and reading precision.
Moreover, the application has also proposed that in order to improve the fluidity, etc., dried silica fine powder which has been treated by a silane coupling agent and silicone oil should be externally added thereto.
However, although the MICR toner, which has been proposed in Japanese Patent Application No. 137153/1998, is superior in the initial image density and reading precision, the reading precision gradually drops as sheets of A-4 paper are continuously printed, and the reading precision tends to become not more than 80% when approximately 50,000 prints have been made. Consequently, with respect to MICR toner that satisfies the long-term printing property required for the application of an amorphous silicon photosensitive member, that is, for example, the endurance of continuous printing of 150,000 to 300,000 sheets of A-4 paper, this toner is insufficient in its durability.
Moreover, in the case where the dried silica fine power is externally added to the MICR toner, since the average particle size of the dried silica fine powder is small, it fails to provide sufficient abrasive effects, and the external application of the dried silica fine powder causes an increase in the quantity of charge, resulting in failure to provide sufficient conductivity controlling effects. Therefore, in the case where the dried silica fine powder is externally applied, much adhesive powder such as toner fine powder, paper powder and a mixture of these tends to remain on the amorphous silicon photosensitive member, after continuous printing processes of approximately 50,000 sheets of A-4 paper.
The objective of the present invention is to provide an MICR toner, a developer for MICR printers and a manufacturing method thereof, which allow the MICR toner itself to exert abrasive effects so as to reduce the amount of adhesive powder such as toner fine powder, paper powder and a mixture of these remaining on an amorphous silicon photosensitive member, and also allow the MICR toner to exert conductivity regulating effects so that, even after, for example, 150,000 to 300,000 sheets of A-4 paper have been continuous printed by using an electrophotographing apparatus having an amorphous silicon photosensitive member, etc. with a SiC surface, it provides superior image density and reading precision.
The inventors, etc. of the present invention have studied hard and found that, when metal oxide particles having a specific volume resistivity are fixed onto the outer surface of MICR toner (toner base particles), the resulting metal oxide particles, when applied to an amorphous silicon photosensitive member having a silicon carbide (SiC) surface, etc., exert particular abrasive functions, and superior conductivity regulating functions so that the MICR toner itself is allowed to scrape MICR toner remaining on the photosensitive member to improve the durability and also to effectively prevent a so-called image blurring phenomenon.
A first aspect of the present invention provides a magnetic toner for MICR printers which comprises a binder resin, magnetic powder and metal oxide particles which are in the outer surface of each toner base particle made from the binder resin and the magnetic powder, the metal oxide particles having a volume resistivity of 1xc3x97105 to 1xc3x971011 xcexa9xc2x7cm.
In other words, the above-mentioned arrangement allows the MICR toner itself to exert abrasive effects, and makes it possible to strictly control the conductive stability of the MICR toner; thus, it becomes possible to greatly improve the image density and durability with respect to reading precision.
Moreover, upon forming the MICR toner of the present invention, it is preferable to provide the following arrangements:
(1) A part of the metal oxide particles are exposed.
(2) The metal oxide particles have an average particle size of 50 nm to 1 xcexcm.
(3) The hardness of the metal oxide particles is 5 to 7.5 in Moh""s hardness.
(4) The addition amount of the metal oxide particles is 0.1 to 2% by weight of an entire amount.
(5) The kinds of the metal oxide particles are aluminum oxide (alumina), titanium oxide (titania), or combination thereof.
With the above-mentioned arrangements, it is possible to allow the MICR toner itself to exert further superior abrasive effects, and also to provide a better conductivity controlling property.
Moreover, upon forming the MICR toner of the present invention, the magnetic powder is preferably prepared as a mixture of first magnetic powder having a residual magnetization of 24 to 40 emu/g and second magnetic powder having a residual magnetization of 1 to 24 exclusive emu/g (i.e., 1 inclusive to 24 exclusive emu/g).
With this arrangement, it is possible to greatly improve the dispersing property of the magnetic powder in the MICR toner, and consequently to improve the image density and the reading precision.
Moreover, a second aspect of the present invention provides a manufacturing method of a magnetic toner for MICR printers comprising the steps of forming a toner base particle by mixing a binder resin and magnetic powder and adding metal oxide particles having a volume resistivity of 1xc3x97105 to 1xc3x971011 xcexa9xc2x7cm to the outer surface of each toner base particle.
Furthermore, upon carrying out the manufacturing method of the MICR toner, the metal oxide particles are preferably fixed to the outer surface by using a fluidizing mixer, a mechanical fixing device, a high-speed air-flow impact fixing device or a thermal fixing device.
The application of each of these fixing devices makes it possible to easily fix the metal oxide particles onto the outer surface with a part of each particle being exposed.
Moreover, a third aspect of the present invention provides a developer used for MICR printers, which comprises the MICR toner of the first aspect and a carrier.
In other words, since predetermined metal oxide particles are contained, it is possible to allow the MICR toner itself to exert abrasive effects, and also to strictly control the conductivity of the MICR toner; thus, it becomes possible to greatly improve the image density and the durability with respect to the reading precision.
Moreover, the carrier is mixed into the MICR toner so as to form a two-component-type developer for MICR printers; thus, as compared with one-component-type developer, it is possible to further improve the transporting property and the image density, etc., of the MICR toner.
Furthermore, since the transporting property of the MICR toner is improved by the functions of the carrier, the selectable range and permissible range of the kinds, addition amount and other factors of magnetic powder that is usable for MICR toner are widened.
Moreover, in the developer for MICR printers of the present invention, the following arrangements are preferably adopted so as to allow the MICR toner itself to exert superior abrasive effects and also to allow the MICR toner to have a better conductivity-controlling property.
(1) A part of the metal oxide particles are exposed.
(2) The metal oxide particles have an average particle size of 500 nm to 1 xcexcm.
(3) The hardness of the metal oxide particles is 5 to 7.5 in Moh""s hardness.
(4) The addition amount of the metal oxide particles is 0.1 to 2% by weight of an entire amount.
(5) The kinds of the metal oxide particles are aluminum oxide (alumina), titanium oxide (titania), or combination thereof.
Moreover, upon forming the developer for MICR printers of the present invention, the magnetic powder in the MICR toner is preferably prepared as a mixture of first magnetic powder having a residual magnetization of 24 to 40 emu/g and second magnetic powder having a residual magnetization of 1 to 24 exclusive emu/g.
With this arrangement, it is possible to greatly improve the dispersing property of the magnetic powder in the MICR toner, and consequently to improve the image density and the reading precision as well as greatly improving the transporting property of the MICR toner.
Moreover, upon forming the developer for MICR printers of the present invention, it is preferable to externally add magnetic powder carrier and resin coat carrier, or either one of these, to the MICR toner.
With this arrangement, it is possible to greatly improve the transporting property of the MICR toner, and consequently to improve the image density and the reading precision.
Furthermore, a fourth aspect of the present invention provides a manufacturing method of developer for MICR printers, which comprises the steps of forming a toner base particle by mixing a binder resin and magnetic powder, adding metal oxide particles having a volume resistivity of 1xc3x97105 to 1xc3x971011 xcexa9xc2x7cm to the outer surface of the toner base particle to form a MICR toner, and mixing the MICR toner and a carrier.
Moreover, upon carrying out the manufacturing method of the developer for MICR printers, the metal oxide particles are preferably fixed to the outer surface of the toner base particle by using a fluidizing mixer, a mechanical fixing device, a high-speed air-flow impact fixing device or a thermal fixing device.
The application of each of these fixing devices makes it possible to easily fix the metal oxide particles onto the outer surface thereof with a part of each particle being exposed, and consequently to provide better controls on the abrasive effects and conductivity of the MICR toner.
Furthermore, a fifth aspect of the present invention provides a magnetic toner for MICR printers, which is obtained through the manufacturing method of the second embodiment.
Moreover, in accordance with the MICR toner of the present invention and the developer containing the MICR toner, the metal oxide particles, which have a volume resistivity of 1xc3x97105 to 1xc3x971011 xcexa9xc2x7cm, are fixed onto the outer surface of the MICR toner; thus, it is possible to provide superior abrasive effects and charge adjusting effects so that, for example, even after 150,000 to 300,000 sheets of A-4 paper have been continuously printed, it is still possible to provide superior image density and reading precision with respect to MICR fonts.
Furthermore, in the case of the MICR toner and developer in accordance with the present invention, even when applied to an amorphous silicon photosensitive member, etc., having a hydrophilic SiC surface, they make it possible to provide particular abrasive effects and superior conductivity controlling functions so that the MICR toner itself is allowed to scrape MICR toner remaining on the photosensitive member, and also to effectively prevent a so-called image blurring phenomenon.
In accordance with the manufacturing method of MICR toner and developer of the present invention, it is possible to efficiently provide MICR toner and developer which, for example, even after 150,000 to 300,000 sheets of A-4 paper have been continuously printed, still make it possible to provide superior image density and reading precision.